cardiac class

the heart is a muscle divided into four chambers

right and left atria are intake chambers and conduits for blood

left and right ventricles are the pumps for propelling the blood

automaticity

cardiac cells generate their own electrical impulses

conductivity

the ability of cardiac cells to conduct an impulse to other cardiac cells

excitability

ability for cardiac cells to respond to electrical stimuli

contractility

ability for cardiac cells to shorten (contract)

rhythmicity

characteristic of the electrical conduction system to form impulses at regular intervals

SA node

right atrium near superior vena cava

initiates electrical impulses at a rate of 60-100 BPM

Internodal tracts/pathways

Pathways between SA and AV node

conducts impulse bw SA to AV

AV node

inferior right atrium that slows conduction down to the ventricles (only normal route of impulse from internodal tracts to bundle of his)

backup pacemaker at 40-60 BPM

Bundle of HIS

intraventricular septum that conducts impulses to the right and left ventricles

backup backup pacemaker at 20-40 BPM

Purkinje fibers

extends from bundle branches to. the muscular walls of the venricles

conducts impulses to venticular muscle cells

20-40 BPM

SNS

increases automaticity

increases speed of conduction

increases contractility

*anxiety

*heart failure

PSNS

decreases automaticity

decreases speed of conduction

decreases contractility

*vagal responses activates

pain can activate vagal response
choking

cardiac output

Heart rate x Stroke volume

good= 4-6 L/min

Bad=< 3 L/min

low cardiac output

ams, loc, cold skin, pallor, chest pain, pressure, SOB, low uop, low BP

depolarization

wave of electrical energy conducted cell to cell in the heart causing contraction of the heart muscle

repolarization

the return of the elctrical charges to the original, resting state causing relaxation of the heart muscle

Order of cardiac cycle

1. SA depolarizes

2. atria depolarize

3. atria contract

4. AV delays conduction

5. ventricles depolarize

6. ventricles contract

7. ventricles repolarize

8. ventricles relax

direction that electrical current

flows from the heart from the right shoulder to the left hip

when electricity goes towards the positive lead

positive waveform happens

when electricity flows away from the positive lead

a negative wave form happens

when current flows towards and away from the positive lead

a biphasic waveform happens

lead II

positive on left leg

negative right arm

identifies atrial activity

p waves usually positive, qrs usually positive

Lead V1

positive electrode in the fourth intercostal space, right sternal border

uses other leads on the chest as the negative

used to differentiate wide complex tachycardias and bundle branch blocks

p waves are negative positive or biphasic

QRS COMPLEXES NEGATIVE

BROWN LEAD 4th INTERCOSTAL SPACE RIGHT STERNAL BORDER

EKG paper

each small box 0.04 seconds

five small boxes make up one large box 0.20 seconds

p wave

depolarization of the atria (time it takes to go from SA down the tract

first waveform before qrs

PR interval

represents the time for the electrical impulse to spread through the atria and the AV node

reflects slowing of the electrical impulse to allow for ventricular filling

measured from the beginning of the pwave to the begining of the qrs

NORMAL 0.12-0.20 seconds

SA→AV node

QRS complex

conduction of electrical impusle from AV through the ventricular muscle depolarization of the right and left ventricles

NORMAL IS LESS THAN 0.12 SECONDS.

if qrs > 0.12 seconds, abnormal depolarization and conduction of energy flow through the heart.

T wave

ventricular repolarization

ST segment

time it takes for complete ventricular depolarization to the beginning of repolarization, normally isometric (can be elevated or depressed.

elevation and depression=signs of ischemia.

QT interval

represents depolarization and repolarization of the ventricles

measured from beginning of qrs to end of the t-wave. (t-wave ends when it returns to baseline.)

normal is less than 0.50 seconds. Notify provider if > 0.50 seconds

elongated QT= predisposure to deadly dysrhthmias

**TRENDS

refractory periods

time in the cardiac cycle when heart cannot respond to elelctrical stimulation because it has not recovered from depolarization

absolute refractory=during first portion of t-wave

relative refractory=downslope of the t-wave

MOST VULNERABLE